On 2/8/2020 3:37 AM, Bertrand Augereau wrote:
  :
I spawn my subprocess with subprocess : https://docs.racket-lang.org/reference/subprocess.html And for the sake of completeness I want to know when suprocess failed (because the users tampered with the exe, because there's an ACL issue, whatever). The function doesn't have a return value for failure and it doesn't raise an exception when I do stuff like
(subprocess "no exe here")
or
(subprocess "nice picture of an aardvark.png")
It only returns a seemingly valid value.

The 1st value returned by (subprocess) is an opaque reference to the executing process.  If you pass the reference to (subprocess-status) it will return *'running*  if the process currently is executing, or the exit/error value.


Can someone help me ? Is it an API defect and a special value should be returned ? Should an exception be raised ? The doc doesn't say much about this.

A special value is returned - the opaque reference.  Perhaps the docs could use a simple example of how to use the functions effectively.  Try playing a bit with the following:

   #lang racket

   (define sub #f)

   (let [
          (name "C:\\WINDOWS\\system32\\notepad.exe")
          (in #f)(out #f)(err #f)
         ]
      (set!-values (sub out in err) (subprocess #f #f #f name))
      )

   (subprocess-status sub)
   (subprocess-pid sub)

   (subprocess-wait sub)
   ;; close subprogram here

   (subprocess-status sub)
   (subprocess-pid sub)



I don't really care about the OS-level cause of the failure but I need to know if it failed.
I didn't test on my Linux box for consistency.

By the way, subprocess-pid returns 0 on such a "never spawned" process, and I think it should be an error case too.

No actual process can have pid 0 ... that value is reserved  (on Unix/Linux and Windows).

Racket doesn't support fork (because Windows doesn't), but recall that when you fork in Unix/Linux, the child process receives the illegal pid value 0 so that it knows it is the child, while the parent receives the real pid value for the child.

Also note that (subprocess-pid) will be valid only if the process started successfully.


Hope this helps,
George

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